1. Field of the Invention
The invention relates to a planetary rotation machine having a displacer part acting as a drive part or power take-off part and a control part that serves for supplying working fluid to, and removing working fluid from, the displacer part and rotates relative to at least one adjacent bearing part about an axis of rotation of the control part. The displacer part has a stationary outer part with an inner tooth system that interacts with an outer tooth system of a rotatable, eccentrically arranged rotary piston. Transmission means are provided that transmit the rotary velocity of the rotary piston about its own axis with the same torque to a drive shaft or power take-off shaft. The invention also relates to a control part with a slide bearing for such a planetary rotation machine. These planetary rotation machines preferably operate as low-speed machines with high thrust according to the so-called orbit principle. Hydrostatic, in particular oil-operated, planetary rotation machines are primarily meant. However, the invention can also be applied in the case of machines which are operated with a compressible working medium, in particular with compressed air.
2. Discussion of Relevant Art
For controlled feed of the working fluid in the displacer part, these machines have rotary valves or rotating control parts which revolve at the speed of the rotor or planetary piston. A control part comprises essentially two annular channels which are open to the outside towards a contact region. The high pressure side of the two working fluid connections is connected to one channel, and the low pressure side to the other. In the control part, connections extend alternately from the two annular channels into a common connection region, from which connecting lines lead through a connection part to the displacer part. The annular channels and the connection region are in sliding contact with the connecting lines or with contact surfaces in which the line connections are arranged. The transport of working fluid in as leak-free a manner as possible under pressure between parts moving relative to one another or through sliding bearings requires distances as small as possible between the sliding surfaces. However, the distances may not be so small that high frictional losses and in particular considerable wear result. It has been found that the total losses of planetary rotation machines are due to a large extent to the losses at the rotating control parts.
In general, spool or disc valves are used as control parts. The sliding connection regions and the annular channels are arranged at cylindrical lateral surfaces in the case of spool valves and at least the majority of them are arranged at the flat side surfaces normal to the axis of rotation of the control part in the case of disc valves. If necessary, an annular channel may be formed along the cylindrical lateral surface also in the case of disc valves. The alternating connections to the common connection region preferably lead through the disc and are thus not arranged in the region of the sliding bearing.
In the rotating state at high speeds, the spool valves have a relatively high resistance to flow owing to the associated increase in the turbulence of the fluid flowing through the channels and connections. Preferably, mounting is effected by means of the cylindrical spool outer surface sliding against a cylindrical inner surface of a housing part. If the so-called port-to-port leaks are kept small, the play in the housing must be extremely small, preferably less than 0.5 per mil of the spool diameter. Since the cylinder surface interrupted by channels does not have good properties as a sliding bearing, wall contact cannot be avoided. As a result of wear and erosion, the play increases very rapidly during operation, so that the channel leaks and also the drainage leaks into the machine interior increase rapidly.
In the case of disc valves, the flat disc end surfaces must be mounted optimally and without leaks and friction. The requirement for the radial mounting and for the cylinder lateral surface depends on whether annular channels and sliding connections are to be provided thereto. Since, however, the alternating connections to the common connection region are not in the region of the cylinder lateral surface, better sliding bearing properties can be achieved even when radial outer mounting is envisaged than in the case of conventional spool valves. In order to achieve better efficiency and a longer service life at high operating pressures, disc valves are increasingly being used. In an expedient embodiment of the connections, the disc valves have a smaller flow resistance compared with the spool valves.
In the case of disc valves, it is possible to achieve minimum play and compensation of wear by adjusting an axially adjacent part. Wear is compensated by providing, for example, a compensation piston which, in both directions of rotation, presses the disc valve without play against the connection part with the connecting lines to the displacer part. However, relatively high undesired frictional losses occur, amounting to as much as 12 percent of the theoretical torque. In addition, the losses are of different magnitudes in the forward and backward directions.
The known control parts are hydrodynamically mounted, that is to say the friction is high particularly during start-up of the planetary rotation machine. In the operating state, a lubricating layer forms in the bearing. In the event of vibrations due to variable loads or due to movement of the planetary piston, direct contacts between the sliding surfaces occur in spite of the lubricating layer in the bearing.
It has been found that an unexpectedly large part of the power loss of the planetary rotation machines is accounted for by the rotating control parts which, in accordance with their formation, are designated as spool or disc valves.